a group of participants, treatments, or situations selected from a larger group

a selection of people or items from the population

easier/quicker to use

Population

refers to all people or items with a particular characteristic of interest

the larger group from which a sample is taken

Systematic sampling

i.e picking every 100th name in phone book

select a sample for telephone interviewing by selecting every 20th name in the student directory

Stratified random sampling

Method of stratifying a population on some characteristic before random selection of the sample

i.e picking 20 males from 1000 random 20 females from 1000 random

Random assignment

i.e assign id numbers to clients pick clients at random

Post Hoc

Justification that the sample repressents some groups at large

Central tendancy

a single score that best represents all the scores

Indication of the typical score in a data set

– Mean – Median – Mode

Variability

the degree of difference between each individual score and the central tendency score

measures of how scores vary

– Range – Interquartile range – Standard deviation

Standard Deviation

an estimate of the variability of the scores of a group around the mean (Rmpa)

measure of how much the score varies around the mean

*spread of scores about the mean

gives us the average amount by which the scores deviate from the mean

Variance

the square of the standard deviation

Mean

Most frequently used measure of central tendency

add all numbers divide by sum of participants

influenced by extremes

Median

middle of all scores in order

Mode

most frequent score occuring

Range

Highest- lowest

variability score

Confidence Interval

Present an interval estimate of the population mean

Indicates the interval within which we are confident the population mean will fall

Centered around the sample mean

Provies an expected upper and lower limit for a statistic at a specified probability level

Can be represented in error bar charts

Normal Curve

Distribution of data in which the mean, median and mode are at the same point.

and in which is from the mean includes

Skewness – Kurtosis

68% of the scores 1+ from the means

95% 2+ from score and 99% is 1+

Parametric statistics

Normal distribution Equal variances – Independent observations

Test based on data assumptions of normal distribution equal variances and independent observations

Non- Parametric Statistics

Distribution is not normal

any of a number of statistical techniques used when the data do not meet the assumptions required to perform parametric

Statistical power

the probability of rejecting a false null hypothesis

The probability of making a correct decision!

Directly related to the probability of making a type II error

Skewness

description of the dirction of the hump of the curve of the data distribution and the nature of the tails of the curve

*term that describes the position of the hump in the curve of a distribution is

side to side

Left positive skewness

Right negative skewness

Kurtosis

Description of the vertical characteristics of the curve

Whether the curve is more peaked or or flatter

Statistical Significance

A criterion for significance is set

This is usually a probability set at .05

if our calculated p-value is less than the criterion for significance

This is classed as ‘statistically significant’

Meaningfulness

The importance or practical significnat of an effect or relationship

Probability

Odds that a certain event will occer

P-value

The probability that your results are due to chance or sampling error

chance your results are due to chance or sampling error

Null hypothesis

a statement of no difference or no relationship.

statistical hypothesis that assumes that there is no difference among the effects of treatments

i.e There is no difference between the vocabulary scores of average- and high-ability students.

alpha a/ level of significance

level of probability set by the experimenter before the study

type 1 error

rejecting the null hypothesis when its true

probability of making a Type I error is denoted by the alpha (α)

researcher claims that there is a difference between treatments (i.e., rejects the null hypothesis) when there really is no difference

Type 2 error

accepting the null hypothesis when its true

a Type II error is denoted by the beta (β) level

Beta

Magnitude of a type 2 error

Sample size

the number of participants in the study being evaluated or planned

Effect size/ delta

the outcome of a study typically expressed in standard deviation units

standardized value that is the difference between the means divided by the standard deviation

Meaningfulness The size of the difference (Cohen’s d)

the strength of the relationship (r2)

standard error

variability of the sampling distribution

Descriptive statistics

statistical techniques which helps us describe data

Inferential statistics

statistical techniques devised to allow us to generate from our data to populations

Quartiles

values which divides data set into exactly 4 equal parts

variance

the average of the squared deviates from the mean

cluster sampling

sampling where the population is divided into smaller identifiable clusters and one or more of these cluster are then randomly selected. Participation are then randomly selected from smaller cluster to take part in a study

Opportunity sampling

sampling from those people who are available at a particular time and place

snowball sampling

a sampling technique where individuals who have taken a part in a study provide detail of people they know who might also be willing to participate

Volunteer sampling

sampling which relies on participants coming forward to volunteer to take part in a study usually in response to an advertising

sampling error

bias in the estimation of population paremeters that arise from using samples

parameters

statistical descriptions of populations

statistics

description applied to samples

chance

same as probality odds of something happening

normal distribtution

a distribution of a scores which is symmetrical peaked in the middle, is bell shaped and equal on both sides of the peak

Bi-directional/ two-tailed hypothesis

Suggests a difference or relationship but not the specific direction of these

*researcher predicts that there will be a difference between 2 groups but is unable to predict which group will score higher than the other

There will be a difference between hearing aid and control groups in social anxiety scores

a hypothesis where we have not specified the direction of the predicted difference or relations

Directional, uni/one-tailed hypothesis

States the direction of the difference or relationship

ie. the hearing aid group will have lower social anxiety than the control group